Cellular telephony systems provide coverage across broad areas using cells, where each cell is serviced by a corresponding cellular base station. A conventional base station is located adjacent the bank of antennas and amplifiers the base station uses to service its cell. As cellular providers support increasingly sophisticated services such as 3G (the third generation of standards for mobile networking), the real estate demands for the base stations necessary to support each cell in a cellular network increase. The costs for the space necessary to store the base station as well as the manufacturing costs for the base station itself motivated a cellular telephony consortium to develop a standardized interface denoted as the Common Public Radio Interface (CPRI). In a CPRI system, the base stations, which comprise part of what is referred to as Radio Equipment Control in a CPRI system, are located remotely from the cellular amplifiers and antennas; the amplifiers and antennas being part of what is denoted as Radio Equipment in a CPRI system. CPRI thus enables a distributed architecture in which the Radio Equipment Control (REC) base station functionality is coupled to corresponding Radio Equipment (RE) through fiber optic or wired links. In this fashion, a CPRI base station need not be located in a costly (and environmentally challenging) location such as urban rooftops or adjacent power station towers that hold the CPRI RE (also denoted as the Radio Head). In addition, the standardized nature of CPRI offers inherent cost savings to cellular providers as equipment providers must directly compete with each other because they offer the same standardized equipment. As a result, cellular telephony systems organized according to the CPRI protocol are growing in popularity.
In the CPRI standard, user data from the Radio Head is mapped into CPRI basic frames according to Antenna-Carrier (AXC) groups, where each AC group corresponds to one carrier at each independent antenna element. The CPRI standard defines a standard interface between the RE and the REC such that the in-phase (I) and quadrature phase (Q) digital samples that comprise the user data from the RE/radio head are mapped into CPRI basic frames according to this CPRI interface. While the structure of the CPRI basic frame is defined by the CPRI standard, the mapping of the IQ user data into AXC groups (also denoted as AC containers) within the CPRI basic frame is left as an implementation detail to the individual user. This mapping will depend on variables such as the sample width (number of bits) for the IQ data data words, the AXC bandwidth, and the CPRI line rate (in Mbps). In that regard, specific mappings have been developed for the various wireless services such as Worldwide Interoperability for Microwave Access (WiMAX), Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE), and the like. But each service will typically need a unique mapping. For example, LTE specifies IQ sample widths of 4 to 20 bits in the uplink direction and 8 to 20 bits in the downlink direction.
Accordingly, there is a need in the art for a flexible mapping implementation to map IQ user data into standardized frames.